Both off-site and on-site sewer mains of not less than eight (8) inches in diameter shall be installed in such a way that each lot may be served therefrom. Sewer laterals shall be not less than four (4) inches in diameter and shall be installed from the sewer main to the lot line of every lot. Sewer laterals serving two (2) lots or two (2) dwelling units shall be not less than six (6) inches diameter and sewer laterals serving more than two (2) lots or two (2) dwellings shall be not less than eight (8) inches diameter. The sewer system shall have a letter of approval from the Department of Environmental Quality and the local health department. (PZSC § 06-28-006 (2))